Leaflet

Leaflet

Introduction to Leaflet in R

Basic Usage

Create map widget with leaflet()

library(leaflet)
library(sf)

Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1

beetle_url <- "https://raw.githubusercontent.com/dyerlab/ENVS-Lectures/master/data/Araptus_Disperal_Bias.csv"
beetle <- read.csv(beetle_url)

beetle <- beetle %>%
   st_as_sf( coords=c("Longitude","Latitude"), crs=4326 )

Add a basemap with addTiles(). By default OpenStreetMap tiles are used.

leaflet() %>%
  setView(lng = -77.5, lat = 37.5, zoom = 10) %>% #not necessary to set your view
  addTiles()

#blank map because we haven't added any layers

Third party tiles

Use addProviderTiles() function to use a different basemap.

See here for all options

leaflet() %>%
  setView(lng = -77.5, lat = 37.5, zoom = 10) %>% #not necessary to set your view
  addProviderTiles(providers$CartoDB.Positron)

Data Objects

• dataframe with lat/lng columns
• sp objects
• sf objects
• maps package map() objects

Data can be passed through the leaflet() function or through the map layers.

#These make the same map

leaflet(beetle) %>%
  addTiles() %>%
  addCircles()

leaflet() %>%
  addTiles() %>%
  addCircles(data = beetle)

Points, lines and Polygons

Points can be plotted using addMarkers() or addCircles() - Markers stay the same size regardless of zoom level - Circles scale with the map

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addMarkers()

Custom Markers - Custom markers can be made using a url/image file or from libraries

bug <- icons(
  iconUrl = "https://www.pngfind.com/pngs/m/14-144860_beetle-bug-png-transparent-image-bug-png-png.png",
  iconWidth = 20,
  iconHeight = 20
)

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addMarkers(icon = bug)

link to Font Awesome library

fa_bug <- makeAwesomeIcon(icon = "bug", library = "fa", 
                          markerColor = "cadetblue", iconColor = "beige")

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addAwesomeMarkers(icon = fa_bug)

Popups can be added as a stand-alone feature using addPopups(), or add to appear when a shape is clicked

#stand-alone

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  setView(lng = -111, lat = 25, zoom = 7) %>%
  addPopups(lng = -111, lat = 25, paste0("beetles live here"))

#as a part of a marker

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addAwesomeMarkers(icon = fa_bug, popup = paste0("Site:", beetle$Site))

Labels

Use label = to add a label displayed on a mouse over

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addAwesomeMarkers(icon = fa_bug, label = paste0("Site:", beetle$Site))

addCircles()

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircles()

Change radius:

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircles(radius = ~Males *500, stroke = FALSE, fillOpacity = .5)

Change color:

pal <- colorNumeric(
  palette = "RdBu",
  domain = beetle$MFRatio
)


leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircles(color = ~rev(pal(MFRatio)), fillOpacity = .7, radius = 15000, stroke = FALSE)

Highlight

leaflet(beetle) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircles(fillColor = ~rev(pal(MFRatio)), fillOpacity = .7, radius = 15000, 
             weight = 1, color = "grey",
  highlightOptions = highlightOptions(color = "green", weight = 2,
      bringToFront = TRUE))

Polygons

library(tidyverse)

-- Attaching packages --------------------------------------- tidyverse 1.3.0 --

v ggplot2 3.3.3     v purrr   0.3.4
v tibble  3.0.5     v dplyr   1.0.4
v tidyr   1.1.2     v stringr 1.4.0
v readr   1.4.0     v forcats 0.5.1

Warning: package 'dplyr' was built under R version 4.0.4

-- Conflicts ------------------------------------------ tidyverse_conflicts() --
x dplyr::filter() masks stats::filter()
x dplyr::lag()    masks stats::lag()

library(tigris)

To enable 
caching of data, set `options(tigris_use_cache = TRUE)` in your R script or .Rprofile.

options(tigris_use_cache = TRUE)

tracts <- tracts("VA", "Richmond city") %>%
  st_transform(4326)

leaflet(tracts) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addPolygons()

Add scale bar with addScaleBar()

pal <- colorNumeric(palette = "Blues",
                    domain = tracts$ALAND/2.59e+6)

leaflet(tracts) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addPolygons(fillColor = ~pal(ALAND/2.59e+6),  fillOpacity = 1, smoothFactor = .2,
              color = "darkgrey", weight = 1,
                highlightOptions = highlightOptions(color = "white", weight = 2, opacity = 1,
                bringToFront = TRUE),
              label = paste(round(tracts$ALAND/2.59e+6, digits = 2), "sq. mi.")
              ) %>%
  addLegend(pal = pal, values = ~ALAND/2.59e+6, title = "Area (sq. miles)") %>%
  addScaleBar(position = "bottomright")

Leaflet Extras

addDrawToolbar()

library(leaflet.extras)

leaflet(tracts) %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addPolygons(fillColor = ~pal(ALAND/2.59e+6),  fillOpacity = 1, smoothFactor = .2,
              color = "darkgrey", weight = 1,
                highlightOptions = highlightOptions(color = "white", weight = 2, opacity = 1,
                bringToFront = TRUE),
              label = paste(round(tracts$ALAND/2.59e+6, digits = 2), "sq. mi.")
              ) %>%
  addLegend(pal = pal, values = ~ALAND/2.59e+6, title = "Area (sq. miles)") %>%
  addScaleBar(position = "bottomright") %>%
  addDrawToolbar()